Aircraft and other vehicles utilize fasteners in fuel tanks and other areas in which electromagnetic effect (EME) phenomena, e.g. lightning strikes, are a concern. To protect against EME phenomena, seals are conventionally installed over the fasteners to satisfy electrical-insulation and other sealing requirements. Regulations provide specific parameters for the geometry and consistency of such seals.
Manually applying the sealant with a conventional daubing gun may result in non-uniform seals containing varying volumes of sealant. Moreover, conventional daubing guns used to apply the sealant often utilize compressed air for sealant ejection. The compressed air may mix with the sealant, introducing air bubbles into the sealant. Air bubbles remaining in the sealant after curing create voids that negatively affect the EME protection capabilities of the seal, requiring replacement or correction.
Seal caps are often used instead of manually applying the sealant. Seal caps include exterior shells filled with viscous sealant. Each seal cap is pressed over a fastener until sealant is squeezed out of the shell. Squeeze out must be removed or smoothed, which increases cycle time and potential for time-consuming rework. Moreover, air may become trapped underneath the shell, which is undesirable for the reasons explained above.